Zoom lens and optical imaging device including the same

ABSTRACT

A zoom lens and an imaging optical device including the same, the zoom lens including, sequentially from an object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, wherein the first lens group includes a spherical negative lens and an aspherical positive lens and the second lens group includes a positive lens and a negative lens, the positive lens and the negative lens including three or more aspherical surfaces.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2009-0061726, filed on Jul. 7, 2009, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a zoom lens and an optical imaging deviceincluding the same.

2. Description of the Related Art

Digital still cameras (DSCs) including a solid state imaging device suchas a charge coupled device (CCD) or a complementary metal-oxidesemiconductor (CMOS), or digital video cameras (DVCs) are widely used.In particular, demands for camera modules with mega-pixel resolutionhave increased, and cameras having picture resolution higher than 5million pixels are frequently employed. Optical imaging devices such asdigital still cameras (DSCs) using a CCD or a CMOS, or mobile phonecameras are required to have small size, light weight, and lowmanufacturing costs.

In order to meet the demands for camera miniaturization, whenphotographing is performed, a lens is extended from or retracted into amain camera body in a predetermined position, and when photographing isnot performed, a collapsible lens barrel that is accommodated in thecamera and is driven to arrange lenses along an optical axis has beenwidely used. In such a collapsible camera, when the collapsible lensbarrel is accommodated in the camera, a distance between lens groupsmust be minimized so that the thickness of a camera can be decreased andportability of the camera can be improved. In the collapsible lensbarrel, the number of lens groups must be decreased in order tomanufacture a small-sized and thin camera. In this case, excellentpicture resolution needs to be ensured.

In order to satisfy these demands, a conventional zoom lens includingthree lens groups has been widely used. Also, a conventional zoom lenssystem including a small-sized photographing lens system having 2× zoomratio has been introduced. In the conventional zoom lens including threelens groups, the first lens group has a negative refractive power, thesecond lens group has a positive refractive power as a whole, and thethird lens group has a positive refractive power, and the three lensgroups are sequentially arranged from an object side to an image side ofthe conventional zoom lens. However, with such a conventional lens it isdifficult to satisfy the demands for miniaturization and low lensmanufacturing costs and also achieve a high zooming rate.

SUMMARY OF THE INVENTION

The invention provides a zoom lens that may be small-sized and may bemanufactured with low manufacturing costs, and an optical imaging deviceincluding the same.

According to an embodiment of the invention, there is provided a zoomlens including, sequentially from an object side, a first lens grouphaving a negative refractive power, a second lens group having apositive refractive power, and a third lens group having a positiverefractive power, wherein the first lens group includes a sphericalnegative lens and an aspherical positive lens and the second lens groupincludes a positive lens and a negative lens, the positive lens and thenegative lens including three or more aspherical surfaces.

According to another embodiment of the invention, there is provided azoom lens, including sequentially from an object side, a first lensgroup having a negative refractive power, a second lens group having apositive refractive power, and a third lens group having a positiverefractive power, wherein the first lens group includes two lenses, andthe second lens group includes an aspherical positive lens and anaspherical negative lens, and the third lens group includes at least onespherical lens having a refractive power that satisfies the followingEquation:

3nd>1.8,

where 3nd is a refractive index of at least one spherical lens of thethird lens group.

The zoom lens may satisfy the following Equation:

16<21vd-22vd<26,

where 21vd is an Abbe's number of a positive lens of the second lensgroup, and 22vd is an Abbe's number of a negative lens of the secondlens group.

The second lens group may correct optical handshake.

All lenses that belong to the first lens group, the second lens group,and the third lens group may include glass.

The negative lens of the second lens group may be convex towards theobject side.

The third lens group may include a positive biconvex lens.

All of the first lens group, the second lens group, and the third lensgroup may be moveable along an optical axis while zooming.

According to another embodiment of the invention, there is provided anoptical imaging device including: a zoom lens; and an imaging sensorreceiving an image formed by the zoom lens, wherein the zoom lensincludes, sequentially from an object side, a first lens group having anegative refractive power, a second lens group having a positiverefractive power, and a third lens group having a positive refractivepower and wherein the first lens group includes a spherical negativelens and an aspherical positive lens and the second lens group includesa positive lens and a negative lens, the positive lens and the negativelens including three or more aspherical surfaces.

According to another embodiment of the invention, there is provided anoptical imaging device including: a zoom lens; and an imaging sensorreceiving an image formed by the zoom lens, wherein the zoom lensincludes sequentially from an object side a first lens group having anegative refractive power, a second lens group having a positiverefractive power, and a third lens group having a positive refractivepower, and the first lens group includes two lenses, and the second lensgroup includes an aspherical positive lens and an aspherical negativelens, and the third lens group includes at least one spherical lenshaving a refractive power that satisfies the following Equation:

3nd>1.8,

where 3nd is a refractive index of at least one spherical lens of thethird lens group.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the invention will becomemore apparent by the following detailed description of exemplaryembodiments thereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a zoom lens at a wide angleposition, a middle position, and a telephoto position, respectively,according to an embodiment of the invention;

FIG. 2A is a chart of aberration at the wide angle position of the zoomlens of FIG. 1;

FIG. 2B is a chart of aberration at the telephoto position of the zoomlens of FIG. 1;

FIG. 3 is a cross-sectional view of a zoom lens at a wide angleposition, a middle position, and a telephoto position, respectively,according to another embodiment of the invention;

FIG. 4A is a chart of aberration at the wide angle position of the zoomlens of FIG. 4;

FIG. 4B is a chart of aberration at the telephoto position of the zoomlens of FIG. 4;

FIG. 5 is a cross-sectional view of a zoom lens at a wide angleposition, a middle position, and a telephoto position, respectively,according to another embodiment of the invention;

FIG. 6A is a chart of aberration at the wide angle position of the zoomlens of FIG. 5;

FIG. 6B is a chart of aberration at the telephoto position of the zoomlens of FIG. 5; and

FIG. 7 is a schematic diagram of an optical imaging device including azoom lens, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The attached drawings for illustrating exemplary embodiments of theinvention are referred to in order to gain a sufficient understanding ofthe invention, the merits thereof, and the objectives accomplished bythe implementation of the invention. Hereinafter, various embodiments ofthe invention will be described in detail with reference to the attacheddrawings. Like reference numerals in the drawings denote like elements.

FIG. 1 is a cross-sectional view of a zoom lens 11 at a wide angleposition, a middle position, and a telephoto position, respectively,according to an embodiment of the invention. Referring to FIG. 1, thezoom lens 11 according to the current embodiment includes a first lensgroup G1 having a negative refractive power, a second lens group G2having a positive refractive power, and a third lens group G3 having apositive refractive power, which are sequentially arranged from anobject side O to an image side I of the zoom lens 11. The first lensgroup G1 may include a first lens 1 and a second lens 2. The first lens1 may have a negative refractive power, and the second lens 2 may have apositive refractive power. The first lens 1 is a spherical lens, and thesecond lens 2 is an aspherical lens.

The second lens group G2 may include a third lens 3 having a positiverefractive power and a fourth lens 4 having a negative refractive power.The fourth lens 4 may be convex towards the object side O. A stop ST maybe disposed at the object side O of the second lens group G2. The thirdlens 3 and the fourth lens 4 may be aspherical lenses. For example, thethird lens 3 and the fourth lens 4 may include three or more asphericalsurfaces and correct aberration that occurs during a zooming operation.The second lens group G2 may include two lenses having a positiverefractive power and a negative refractive power, respectively, so thatchromatic aberration may be easily controlled.

The first lens group G1 affects the viewing angle and diffraction andresolution of the zoom lens 11 at the wide angle position. The secondlens group G2 is related to the zooming rate, and the greater therefractive power of the second lens group G2, the greater the movingrange of the second lens group G2 during zooming. The third lens groupG3 corrects a variation of an image plane caused by a variation of anobject distance, thereby performing focusing. In order to miniaturizethe zoom lens 11 of FIG. 1, the number of lenses needs to be minimized,and also a trajectory of a lens during the zooming needs to beminimized. However, there is a limitation in minimizing the number oflenses or in minimizing the trajectory of the lens. In particular, whenthe number of lenses is decreased, sensitivity with respect to thelenses is increased, and thus the number of aspherical lenses needs tobe increased, and when the number of aspherical lenses is increased,lens manufacturing costs increase. Thus, better aberration and a betteroptical performance are achieved without reducing the number of lensesby using an aspherical lens as a positive lens of the first lens groupG1. By using a negative lens of the first lens group G1 as a sphericallens, the sum of thicknesses of lenses that belong to the first lensgroup G1 may be reduced as compared to a case where the negative lens ofthe first lens group G1 is used as an aspherical lens. A diameter of thenegative lens of the first lens group G1 is greater than a diameter ofthe positive lens of the first lens group G1. In other words, by using apositive lens having a small diameter as an aspherical lens rather thanby using a negative lens having a large diameter as an aspherical lens,the sum of thicknesses of lenses may be reduced. Also, when anaspherical lens is manufactured using a mold, a positive lens having asmall diameter is used as the aspherical lens, and thus productivity maybe improved.

Meanwhile, the third lens group G3 of the zoom lens 11 of FIG. 1 mayinclude at least one lens having a refractive index that satisfies thefollowing Equation 1:

3nd>1.8,  (1)

where 3nd is the refractive index of at least one spherical lens of thethird lens group G3. For example, the third lens group G3 may include afifth lens 5, and the fifth lens 5 may be a spherical lens. The fifthlens 5 has a high refractive index of 1.8 or more so that a properamount of peripheral light may be obtained, an excellent opticalperformance may be obtained, and a thickness of the third lens group G3and an overall length of the zoom lens 11 may be reduced. As a result,the lens barrel may be made slim.

The fifth lens 5 may be a positive biconvex lens. When each of lenses ofthe third lens group G3 is a meniscus lens, the space at a concavesurface of the meniscus lens may be reduced, and an overall length atwhich the lens barrel is extended from or retracted into a main camerabody may be reduced too. In other words, the concave surface of themeniscus lens forms a dead space, and thus, if each lens of the thirdlens group G3 is a meniscus lens, miniaturization of the zoom lens 11 ofFIG. 1 cannot be achieved. Thus, the lens of the third lens group G3 maybe a positive convex lens for miniaturization purposes.

Two filters 6 and 7 may be disposed on the image side I of the thirdlens group G3.

Meanwhile, the second lens group G2 may satisfy the following Equation2:

16<21vd-22vd<26,  (2)

where 21vd is an Abbe's number of a positive lens of the second lensgroup G2, and 22vd is an Abbe's number of a negative lens of the secondlens group G2.

When the Abbe's number of each of the positive lens and the negativelens of the second lens group G2 satisfies the following Equation 2,chromatic aberration may be controlled. When the Abbe's number of eachof the positive lens and the negative lens of the second lens group G2is out of the range defined by Equation 2, color aberration isincreased.

The second lens group G2 in the zoom lens 11 of FIG. 1 corrects imageshake caused by hand shake. In order to correct image shake, the secondlens group G2 is shifted in a direction perpendicular to the opticalaxis. In order to correct image shake, when the second lens group G2 isshifted, the quality of an image needs to be good, and the sphericalaberration and the Petzval sum of the zoom lens 11 need to be properlycorrected. In this case, spherical aberration and eccentric comaaberration that occur in a central portion of a screen when the secondlens group G2 is shifted in the direction perpendicular to the opticalaxis may be suppressed. By correcting the Petzval sum of the zoom lens11, curvature of the image plane that is formed at a circumferentialportion of the screen when the second lens group G2 is shifted in thedirection perpendicular to the optical axis may be suppressed.

All lenses that are included in the zoom lens 11 of FIG. 1 may be formedusing only glass. When all lenses of the zoom lens 11 of FIG. 11 areformed of plastics, lens manufacturing costs may be reduced. However,the number of lenses is small, and thus sensitivity of the lenses may beincreased. Thus, when plastic lenses are used in the zoom lens having asmall number of lenses, excellent optical performance may be difficultto achieve. In order to improve optical performance, the zoom lens 11 ofFIG. 11 may include only glass lenses.

The aspherical shape of the zoom lens 11 of FIG. 11 will now bedescribed. When the optical axis is in an x-axis, a directionperpendicular to the optical axis is a y-axis and a proceeding directionof light is a positive direction, the aspherical shape of the zoom lens11 of FIG. 1 may be given by Equation 3:

$\begin{matrix}{x = {\frac{{cy}^{2}}{1 + \sqrt{1 - {\left( {K + 1} \right)c^{2}y^{2}}}} + {Ay}^{4} + {By}^{6} + {Cy}^{8} + {{Dy}^{10}{\mspace{14mu} {\ldots \mspace{14mu},}}}}} & (3)\end{matrix}$

where x is the distance from the peak portion of a lens to the opticalaxis, y is the distance from the peak portion of the lens to thedirection perpendicular to the optical axis, K is a conic constant, A,B, C, and D are aspherical coefficients, and c is a reverse number 1/Rof the radius of curvature at the peak portion of the lens.

In other embodiments, including the following designs, the zoom lens 11of FIG. 1 may be miniaturized.

Hereinafter, f is the combined focal length of the whole lens system,Fno is the F number, 2w is the viewing angle, R is the radius ofcurvature, Dn is the thickness of a central portion of a lens or adistance between lenses, nd is the refractive index, and vd is an Abbe'snumber, respectively. Also, ST is the aperture stop, and D1, D2, D3, andD4 are variable distances. In the drawings, lenses in a lens group areshown using the same reference numerals.

First Embodiment

FIG. 1 is a cross-sectional view of a zoom lens at a wide angleposition, a middle position, and a telephoto position, respectively,according to an embodiment of the invention.

TABLE 1 EFL: 6.50 to 18.48 mm, Fno: 3.10 to 5.91, Viewing angle: 63.7°to 23.8° Radius of Abbe's Lens curvature Thickness Refractive numbersurface (R) (Dn) index (nd) (vd) S1 92.437 0.500 1.517 52.1 S2 4.7891.088 S3 5.743 1.426 1.821 24.1 S4 7.271 D1 ST infinity 0.000 S6 3.8981.396 1.768 49.2 S7 −18.813 0.110 S8 8.631 0.762 1.821 24.1 S9 2.830 D2S10 200.000 1.408 1.883 40.8 S11 −14.939 D3 S12 infinity 0.300 1.51764.2 S13 infinity 0.300 S14 infinity 0.500 1.517 64.2 S15 infinity D4

The following tables shows the variable distances at which three lensgroups of the zoom lens are moveable along the optical axis when azooming rate is changed from the wide angle position to the telephotoposition, according to the present embodiment.

TABLE 2 Variable Wide angle Middle Telephoto distance position positionposition D1 10.541 4.824 0.992 D2 4.664 9.187 15.193 D3 2.985 2.1551.612 D4 0.600 0.600 0.600

The following represents aspherical coefficients according to thepresent embodiment.

TABLE 3 Lens surface K A B C D S3 −0.690644 −2.061899E−05 −6.329558E−06−1.533885E−06 7.263593E−08 S4 −9.233583 2.151908E−03 −1.988188E−047.151402E−06 −1.177426E−07 S6 −1.040585 8.507990E−04 −1.052304E−06−1.893851E−05 0.000000E+00 S8 0.711831 −3.961101E−03 5.045714E−040.000000E+00 0.000000E+00 S9 −1.000000 1.642222E−03 1.147907E−03−4.533634E−05 0.000000E+00

FIGS. 2A and 2B illustrate spherical aberration, field curvature, anddistortion aberration at the wide angle position and at the telephotoposition of the zoom lens of FIG. 1, respectively. Field curvatureincludes tangential field curvature T and sagittal field curvature S.

Second Embodiment

FIG. 3 is a cross-sectional view of a zoom lens at the wide angleposition, the middle position, and the telephoto position, respectively,according to another embodiment of the invention. The following tableshows actual data about the zoom lens of FIG. 3.

TABLE 4 EFL: 6.49 to 18.44 mm, Fno: 3.2 to 6.0, Viewing angle: 63.9° to23.9° Radius of Abbe's Lens Curvature Thickness Refractive numbersurface (R) (Dn) index (nd) (vd) S1 116.257 0.500 1.517 52.1 S2 4.8921.144 S3 5.798 1.411 1.821 24.1 S4 7.251 D1 ST infinity 0.000 S6 3.9041.373 1.768 49.2 S7 −18.243 0.200 S8 8.345 0.654 1.821 24.1 S9 2.807 D2S10 300.000 1.407 1.883 40.8 S11 −14.640 D3 S12 infinity 0.300 1.51764.2 S13 infinity 0.300 S14 infinity 0.500 1.517 64.2 S15 infinity D4

The following data presents data about variable distances at which thethree lens groups of the zoom lens are moveable along the optical axiswhen the zooming rate is changed from the wide angle position to thetelephoto position, according to the present embodiment.

TABLE 5 Variable Wide angle Middle Telephoto distance position positionposition D1 10.433 4.733 0.962 D2 4.671 9.206 15.219 D3 2.990 2.1731.630 D4 0.600 0.600 0.600

The following table shows aspherical coefficients according to thepresent embodiment.

TABLE 6 Lens surface K A B C D S3 −0.724137 −5.379161E−05 −3.002350E−07−1.781740E−06 9.753703E−08 S4 −8.779591 2.015009E−03 −1.757522E−046.151275E−06 −6.577599E−08 S6 −1.106201 7.136520E−04 −2.239024E−05−1.864413E−05 0.000000E+00 S8 1.118837 −4.127844E−03 6.558722E−040.000000E+00 0.000000E+00 S9 −1.000000 1.414752E−03 1.215779E−03−1.505824E−05 0.000000E+00

Third Embodiment

FIG. 5 is a cross-sectional view of a zoom lens at the wide angleposition, the middle position, and the telephoto position, respectively,according to another embodiment of the invention. The following tablepresents design data about the zoom lens of FIG. 5.

TABLE 7 EFL: 6.56 to 18.87 mm, Fno: 3.4 to 6.4, Viewing angle: 63.3° to22.9° Radius of Abbe's Lens curvature Thickness Refractive numbersurface (R) (Dn) index (nd) (vd) S1 −753.587 0.500 1.513 70.7 S2 5.3901.749 S3 9.640 1.713 1.821 24.1 S4 13.934 D1 ST infinity 0.000 S6 3.9031.573 1.755 40.4 S7 −28.822 0.200 S8 10.671 0.650 1.821 24.1 S9 3.256 D2S10 45.168 1.615 2.001 25.5 S11 −39.733 D3 S12 infinity 0.300 1.517 64.2S13 infinity 0.300 S14 infinity 0.500 1.517 64.2 S15 infinity D4

The following table presents data about variable distances at which thethree lens groups of the zoom lens are moveable along the optical axiswhen the zooming rate is changed from the wide angle position to thetelephoto position, according to the present embodiment.

TABLE 8 Variable Wide angle Middle Telephoto distance position positionposition D1 11.943 4.937 0.882 D2 5.433 9.701 16.358 D3 2.952 2.4821.648 D4 0.600 0.600 0.600

The following table shows aspherical coefficients according to thepresent embodiment.

TABLE 9 Lens surface K A B C D S3 −0.690659 2.135757E−05 −2.301943E−057.822465E−07 −4.538396E−09 S4 −2.126241 −2.786926E−04 −3.334764E−051.427914E−06 −2.839117E−08 S6 −0.705166 1.467241E−03 7.605664E−05−1.743266E−06 0.000000E+00 S7 −10.826915 8.508508E−05 −3.353116E−055.105271E−07 0.000000E+00 S8 −0.545442 −6.052017E−03 3.109667E−040.000000E+00 0.000000E+00 S9 −1.000000 −3.853703E−04 7.154881E−049.064496E−05 0.000000E+00

The following table shows a case where the first through thirdembodiments satisfy Equations 1 and 2.

TABLE 10 First Second Third Equation embodiment embodiment embodimentEquation 1 1.883 1.883 2.001 Equation 2 25.1 25.1 16.3

The zoom lens according to the above-described embodiments has a highzooming rate and may be manufactured to have a small size with lowmanufacturing costs. Also, the zoom lens according to theabove-described embodiments may be used in imaging optical devices suchas digital still cameras (DSCs) using a solid state imaging device suchas a charge coupled device (CCD) or a complementary metal-oxidesemiconductor (CMOS), digital video cameras (DVCs), or mobile phonecameras.

FIG. 7 is a schematic diagram of an optical imaging device including azoom lens, according to an embodiment of the invention. The opticalimaging device according to the current embodiment includes a zoom lensidentical to the zoom lens 11 described above with respect to FIG. 1,and an imaging sensor 12 that receives light formed by the zoom lenssuch as 11 of FIG. 1. The imaging sensor 12 may include a solid stateimaging device such as a CCD or a CMOS. The optical imaging device mayinclude a recording unit 13 recording information about an image of asubject that is photoelectrically converted by the imaging sensor 12,and a finder 14 that observes the image of the subject. In FIG. 7, theoptical imaging device includes the finder 14. The zoom lens of FIG. 1may also be applied to an optical imaging device with no finder. Theoptical imaging device of FIG. 7 may further include a liquid crystaldisplay panel 15 on which the image of the subject is displayed. Theinvention is not limited to this, and the imaging optical device of FIG.7 may be applied to various optical devices except for cameras. In thisway, the zoom lens such as 11 of FIG. 1 is applied to the imagingoptical device such as a digital camera so that an optical device thatis small-sized and in which an image of a subject is picked up with awide angle position at a high zooming rate may be implemented.

As described above, the zoom lens according to this embodiment of theinvention is useful for miniaturization purposes and reducing themanufacturing costs.

In an embodiment, the zoom lens includes three lens groups, therebyhaving a small number of lenses. Also, the first lens group of the zoomlens includes an aspherical lens as a positive lens, and thus thethickness of the zoom lens can be reduced. The third lens group of thezoom lens may include a lens having a high refractive index, and thusthe overall length of the zoom lens can be reduced so that the zoom lensmay be miniaturized.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the following claims.

1. A zoom lens comprising, sequentially from an object side, a firstlens group having a negative refractive power, a second lens grouphaving a positive refractive power, and a third lens group having apositive refractive power, wherein the first lens group comprises aspherical negative lens and an aspherical positive lens and the secondlens group comprises a positive lens and a negative lens, the positivelens and the negative lens comprising at least three asphericalsurfaces.
 2. The zoom lens of claim 1, wherein the zoom lens satisfiesthe following Equation:16<21vd-22vd<26 , where 21vd is an Abbe's number of the positive lens ofthe second lens group, and 22vd is an Abbe's number of the negative lensof the second lens group.
 3. The zoom lens of claim 1, wherein thesecond lens group corrects handshake.
 4. The zoom lens of claim 1,wherein all lenses that belong to the first lens group, the second lensgroup, and the third lens group comprise glass.
 5. The zoom lens ofclaim 1, wherein the negative lens of the second lens group is convextowards the object side.
 6. The zoom lens of claim 1, wherein the thirdlens group comprises a positive biconvex lens.
 7. The zoom lens of claim1, wherein all of the first lens group, the second lens group, and thethird lens group are moveable along an optical axis while zooming. 8.The zoom lens of claim 1, wherein the third lens group performs focusingaccording to a variation of object distance.
 9. A zoom lens, comprisingsequentially from an object side, a first lens group having a negativerefractive power, a second lens group having a positive refractivepower, and a third lens group having a positive refractive power,wherein the first lens group comprises two lenses, and the second lensgroup comprises an aspherical positive lens and an aspherical negativelens, and the third lens group comprises at least one spherical lenshaving a refractive power that satisfies the following Equation:3nd>1.8, where 3nd is the refractive index of the at least one sphericallens of the third lens group.
 10. The zoom lens of claim 9, wherein thezoom lens satisfies the following Equation:16<21vd-22vd<26, where 21vd is an Abbe's number of the positive lens ofthe second lens group, and 22vd is an Abbe's number of the negative lensof the second lens group.
 11. The zoom lens of claim 9, wherein thesecond lens group corrects optical handshake.
 12. The zoom lens of claim9, wherein all lenses that belong to the first lens group, the secondlens group, and the third lens group comprise glass.
 13. The zoom lensof claim 9, wherein the negative lens of the second lens group is convextowards the object side.
 14. The zoom lens of claim 9, wherein the thirdlens group comprises a positive biconvex lens.
 15. The zoom lens ofclaim 9, wherein all of the first lens group, the second lens group, andthe third lens group are moveable along an optical axis while zooming.16. An optical imaging device comprising: a zoom lens; and an imagingsensor receiving an image formed by the zoom lens, wherein the zoom lenscomprises, sequentially from an object side, a first lens group having anegative refractive power, a second lens group having a positiverefractive power, and a third lens group having a positive refractivepower and wherein the first lens group comprises a spherical negativelens and an aspherical positive lens and the second lens group comprisesa positive lens and a negative lens, the positive lens and the negativelens comprising at least three aspherical surfaces.
 17. The opticalimaging device of claim 16, wherein the zoom lens satisfies thefollowing Equation:16<21vd-22vd<26, where 21vd is an Abbe's number of the positive lens ofthe second lens group, and 22vd is an Abbe's number of the negative lensof the second lens group.
 18. An optical imaging device comprising: azoom lens; and an imaging sensor receiving an image formed by the zoomlens, wherein the zoom lens comprises, sequentially from an object side,a first lens group having a negative refractive power, a second lensgroup having a positive refractive power, and a third lens group havinga positive refractive power, and the first lens group comprises twolenses, and the second lens group comprises an aspherical positive lensand an aspherical negative lens, and the third lens group comprises atleast one spherical lens having a refractive power that satisfies thefollowing Equation:3nd>1.8, where 3nd is the refractive index of the at least one sphericallens of the third lens group.
 19. The imaging optical device of claim18, wherein the zoom lens satisfies the following Equation:16<21vd-22vd<26, where 21vd is an Abbe's number of the positive lens ofthe second lens group, and 22vd is an Abbe's number of the negative lensof the second lens group.